Thermal Wave Inspection in IC Manufacturing

We describe a highly sensitive, noncontact method for inspecting important, but previously difficult to monitor, processes used in the manufacture of integrated circuits. This technique, based on the detection of thermal waves through laser-induced modulation of the sample's optical reflectance, has proven to be an excellent means for detecting and quantifying the extent of lattice damage or disorder in silicon and gallium arsenide wafers that results from chemopolishing, ion implantation and etching processes. This technique thus provides a powerful and cost effective method for monitoring the quality of incoming wafers, the dose and uniformity of ion implantations and the efficiency and uniformity of dry etch processes. Furthermore this method may be used on actual product wafers as well as test wafers since the measurements are performed in a completely nondamaging fashion and with micronscale resolution.